A steam-condenser consists of a large number of tubes configured in a nest shape. The number of tubes can be as high as 30,000 in a large power plant condenser. Thermal performance of a condenser is highly dependent on the arrangement of these tubes. This tube nest arrangement shall be capable of reducing the loss of steam side pressure and of removing efficiently the non-condensable gas in the steam. Two-pass condensers are generally used to limit the condenser length. Thermal hydraulics are more complex in a two-pass condenser as approximately two-thirds of total steam condenses on the tubes in the first pass wherein the temperate of the coolant passing through the tubes is comparatively low and the rest of the steam condenses on the tubes in the second pass. U.S. Pat. No. 5,649,590 describes a tube layout in the form of radiating spikes. Some of the spikes split into branches. The branching spikes comprise a base trunk which flares and splits into two branches of equal thickness as soon as the thickness of the trunk of the spike reached between one-and-a-half and two times the thickness of its base. This form of layout makes it possible to install a greater number of tubes in a given area of the tube plate.
Another version of tube nest layout has been disclosed in U.S. Pat. No. 5,960,867. The tube nest is spaced from the bottom surface and the side walls of the vessel so that steam is able to flow from every direction into the tube nest at a reduced velocity. The extracting opening is disposed between the centre of gravity of the outer circumference and the width of each flow passage increases toward the open outer end. The area ratio and the length of flow passage increase toward the center axis of the tube nest. The advantage claimed is a compact condenser capable of reducing pressure loss and efficiently removing non-condensable gas.
U.S. Pat. No. 6,269,867B1 describes a tube nest which has a massed region of cooling tubes and a plurality of tube bundles with flow passages. A non-condensable gas extracting tube is arranged in the massed region. A discharge flow passage if formed at least partially in the tube nest to enable non-condensable gases from the cooling unit or the steam condensing chamber to be discharged outside of the condenser whereby condensing efficiency of the steam contained in the non-condensable gases which flow into the cooling unit or the steam condensing chamber is improved.
A condenser tube nest layout based on church window principle is described in U.S. patent Application publication No. US 2001/0025703A1. The condenser consists of at least one bundle with multiplicity of tubes arranged parallel to one another, the bundle sub-divided into an upper sector and lower sector. A condensate discharge element is arranged in the bundle between the upper sector and the lower sector. This arrangement helps in preventing excessive blockage of steam paths due to condensate raining down.
However, all the prior art tube nest configurations are evolved mainly for single pass steam condensers and these configurations cannot be optimally used for two-pass condensers. Although U.S. Pat. No. 5,649,590 adapts branching spikes concept, the condenser has the disadvantage of possible air pockets formation in spikes as steam enters from both sides of the spike.
The tube nest of U.S. Pat. No. 5,960,967, in which a plurality of flow passages extend from outer circumference towards the extracting opening, suffers from lack of vent lanes.
The tube nest developed based on church window concept and as disclosed in US 2001/0025703, has thick bundle width which results in higher steam side pressure drop.
In a two pass condenser, the available average temperature potential between steam and cooling water is drastically different between the tubes in the first pass and in the second pass. Due to this phenomenon, steam condensation in the first pass is nearly 66% and that in the second pass is 34%. None of the above prior art has considered this phenomenon and hence they are basically applicable to single pass condenser